Overview of surface to near-surface atmospheric profiles over selected domain during the QWeCI project

Abstract

Assessing the evolution of surface to near-surface atmospheric fluxes is key to improving our understanding of their interactions, while further advancing climate applications. In this paper, an overview of the diurnal to seasonal evolution of some surface to near-surface atmospheric fluxes, coupled with their interactions, have been provided. Fluxes of downwelling and upwelling radiation ($SW_\downarrow$, $SW_\uparrow$, $LW_\downarrow$, $LW_\uparrow$), soil heat flux ($\Delta H$), relative humidity (RH), rainfall (RR) and surface air temperature (T), measured from two different locations (Owabi and KNUST) and at a temporal resolution of 10 min, encompassing the quantifying weather and climate impact (QWeCI) Project period (2011–2013), were used to assess their relationship on diurnal to seasonal scales. First, diurnal assessments of the various profiles were performed. These provided information on the relatively active daytime, with the earth surface exposed to substantial $SW_\downarrow$, initiating rising and sinking thermals which subsequently increased T and $\Delta H$, with reductions in RH until few hours after midday, beyond which a reversal was observed. Also, $\Delta H$ from the vegetative terrain (Owabi) was found to be directed into the surface at daytime, and released from the sub-surface layer back into the atmosphere at night time, compensating the energy loss by $LW_\uparrow$ from the surface. Furthermore, rainfall (RR) in both locations were found to be generally convective and occurring mostly between 1500 GMT and 2300 GMT. The relationship between net radiation ($R_N$) and RR is presently statistically unclear, although rainfall peaks were found to be occurring at low $R_N$ and relatively warmer T, accompanied by high RH. Thereafter, seasonal assessments were performed to capture the monthly-averaged diurnal variabilities in the measured surface to near-surface parameters. These showed heightened daytime T, $\Delta H$ and $R_N$, coupled with relatively low RH within the dry seasons, and more reduced profiles within the monsoon season. Additionally, countrywide assessments were performed using ERA-5 datasets which showed similarities with the in situ data. However, convective rains over the domain were not fully resolved in ERA-5. Nonetheless, the findings of this study are essential to understanding surface energy balance processes in tropical, humid climates, which is important for various climate-impact modeling applications and policy formulations over the region.